Aiming at avoiding too large differences in the responses to the environment radioactivity and at establishing a proper revision schedule, almost all radioactivity meters are presently subjected to periodic controls by using a radioactive source, to which the radiameter is manually exposed by an operator, or, in more sophisticated apparatuses, by adopting a radioactive source incorporated with the radiameter itself and by remotely or automatically controlling the apparatus by an operator. Since, during the time period in which the above control action is effected, the radiameter is not operative, said time period should be relatively short and, therefore, the source to be used should have such an activity as to cause the G.M. tube to generate pulses having a high intensity compared to the one generated by the standard environment radioactivity.
The sensitivity monitoring device included in a radiameter according to this invention, in contrast, uses a source that, when it is positioned adjacent to the G.M. tube, it causes a measurement having the same magnitude order as the one caused by the background environment radioactivity to be indicated. Such indication intensity is so low that it cannot be considered under strict legal terms as a radioactive source and, therefore, any biologic damage to the network maintenance personnel or to the station revision personnel is avoided.
The measurement of the activity of said source, which is contemporaneous with the measurement of the environment radioactivity does not jeopardize the response of the radiameter to said environment radioactivity and the measurement operation takes a very long time with respect to the radiameter integration time and, therefore, it is very accurate and enables even minimum sensitivity variations to be automatically corrected. This makes the measurement accuracy in the various stations very uniform and makes the radioactivity topographic maps produced by the environment monitoring network more reliable.
The indication of the sensitivity degradation improves the revision schedule of the stations, thereby making the management of the environment radiametric networks much more cost effective, with respect to all complex and very expensive maintenance operations up to now carried out.
The decay time of the nature occurring radioisotope which is used as the control source is assimilable to infinite and, therefore, it eliminates any need that its measurement values be corrected to compensate the source decay, thereby facilitating the sensitivity controls during the revision operations of the stations.